Pyrolytic conversion of paraffins



Jan. 23, 1962 J. c. KREJcl PYRoLYTIc CONVERSION oF PARAFFINS Filed Sept. 21. 1959 zomm uomo r ww New( runoomaim Nr.5 w IY N E. m53 ozoou 2. mzuj vo HH..

INVENTOR. J.C. KREJCI QN NN United States Patent O 3018 09 rYRoLYrrc coNvfEnsaroN or PARAFFINS Joseph C. Krejcl, Phillips, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Sept. 2l, 1959, Ser. No. 841,380 9 Claims. (Cl. 260-679) This invention relates to the pyrolytic conversion of hydrocarbons containing substantial amounts of aliphatic unsaturated hydrocarbons. A specific aspect of the invention is concerned with the production of ethylene and acetylene.

The invention is an improvement in the process of my U.S. Patent 2,750,434, issued June 12, 1956. The process disclosed and claimed therein comprises pyrolyzing hydrocarbon feed stocks at temperatures in the range of about 1300 to 3500 F. by introducing a preheated hydrocarbon feed axially into a first cylindrical reaction zone of greater diameter than its length contiguous to and coaxial with a secondY cylindrical reaction zone of lesser diameter than the first zone and of greater length than diameter; injecting tangentially into the first reaction zone a combustible mixture of gaseous fuel and oxidant, such as O2 or air; and burning the mixture to form hot combustion gases for heating the feed; passing the feed, initially surrounded by a helically moving annular blanket of said combustion gases, into the second reaction zone, whereby the feed is heated by the combustion gases to a temperature in the range of 1300 to 3500 F. to cause the same to react and form predominantly less saturated hydrocarbons; quenching the efl'iuent from the second reaction zone in a quench zone to a temperature below reaction temperature; and recovering unsaturated hydrocarbons from the quenched etlluent.

I have found that the incorporation of substantial proportions of steam in the hydrocarbon feed in the preheating zone has the multiple advantages of increasing the concentration and yield of unsaturates, particularly, acetylene and ethylene, in the eilluent from the second reaction zone of the reactor, decreasing the carbon deposition in the reactor, and also decreasing the carbon deposition in the quench zone downstream of the second reaction system. It might be expected that the introduction of steam to the precracking furnace would decrease coking therein; however, it was not expected that this introduction of steam would have the beneficial effect of also decreasing the coke deposition in the reactor and in the quench chamber adjacent the eluent end of the second reaction zone.

Accordingly, it is an object of the invention to provide an improved process for pyrolytically converting hydrocarbon feed stocks containing parans to less saturated hydrocarbons with increased yield of unsaturates and higher concentrations thereof in the reaction efuent. Another object is to provide a pyrolytic process for converting hydrocarbon feed stocks to less saturated products with less formation of coke in the reaction system and particularly in the reactor and in the quench chamber adjacent the eluent end of the reaction system. Another object is to reduce coking in a precracking furnace and increase the unsaturates produced therein. Other objects of the invention will become apparent upon consideration of the aompanying disclosure.

The invention comprises incorporating in the feed to the precracking furnace an amount of steam in the range of about 10 to 125 volume percent of the hydrocarbon feed and preheating the mixture to a temperature in the range of 1000 to 1600 F. so as to crack and upgrade a substantial proportion of the hydrocarbon feed, and passing the precracked feed into a reactor of the character described and under the reaction conditions set forth in the aforesaid patent.

3,018,309 Patented Jan. 23, 1862 A more complete understanding of the invention may be had by reference to the accompanying schematic draw. ing of which FIGURE l is a transverse sectional view taken on the line 1-1 of FIGURE 2 and FIGURE 2 is a cross-sectional view of the furnace taken on the line 2-2 of FIGURE 1.

Referring to FIGURE 1, an elongated reaction zone l. is lined with highly refractory material 12, such as corun dum, silica, mullite, zirconia, or sillimanite brick, or other similar suitable materials resistant to high temperatures developed in the reactor. Upstream from and contiguous to reaction zone 10 is a combustion zone 14, axial with zone 10, also lined with refractory material 12. Lining 12 is surrounded by a layer of insulating material 16 and the whole is sheathed in a steel shell 18. Combustion chamber `14 should have a relatively large diameter in comparison to "its length while the reverse is true of reaction chamber 10.

At the upstream or inlet end of combustion chamber 14, a feed inlet tube 20 is arranged axially so that hydrocarbon feed introduced therethru passes axially thru both chambers 14 and 10. Surrounding a portion of feed conduit 20 is a coaxial larger conduit 22 for introducing oxygen or air to the axial feed when this is desired. The arrangement of conduits 20 and 22 defines an annular space thru which oxygen or air may be passed into tube 20 thru holes therein (not shown) so that the fuel and air mixture may be passed axially into chamber 14. A cooling jacket 24 surrounds the inner end of injection tube 20 and is connected with an inlet water line 25 and an outlet water line 26. Water is circulated thru the jacket from line 25 along the length of the jacket and back to outlet line 26. This cooling of tube 20 lengthens its life.

FIGURE 2 shows combustion chamber 14 coaxial with reaction chamber 10 and provided with tangential ports or tunnels 28 spaced 180"V apart. The outer end of tho tunnel 30 is of smaller diameter than the inner portion. A feed inlet pipe 32 is surrounded by a water jacket 34 of the same or similar construction to jacket 24 provided with inlet and outlet lines 36 and 37, respectively. The inlet assembly is positioned so as to inject the feed thru tunnels 30 and 28 into combustion zone 14 where it is burned. Each tangential inlet conduit 32 is connected with an oxygen or air supply line 40 and a fuel gas supply line 42. Most of the tangentially introduced fuel gas is burned in tunnels 28 and chamber 14. Air line 44 and steam line 45 connect with line 46 leading into preheater 48 containing heating coils 50. Line 47 connects the outlet end of heating coil 50 with line 40 leading into feed injection conduit 32. In the event that the steam and air are to be introduced to the tangential burners wihout other preheating than that supplied by the steam, these gases may bypass preheater 48 thru line 52.

Returning to FIGURE 1, a cooling assembly 56 at the eluent end of reaction chamber 10, contiguous and coaxial therewith, comprises a water jacket 58, water-spray 60, water inlet conduit 62 extending thru vthe jacket, a cooling water inlet 64, and a cooling water outlet 66 from jacket space 68. Etlluent hot gases from the reactor are quenched in cooling assembly 56 to below reaction temperature and the quenched gases are passed via conduit 70 to conventional separation means 72 where acetylene is removed thru line 74, ethylene thru line 76, other olens thru line 78, aromatics thru line 86, byproduct paraiins thru line 82, heavy residual materials thru line 84, and water thru line 86.

The axial feed comprising steam and parancontaim ing hydrocarbon materail introduced thru lines 88 and 89, respectively, are introduced to pre-cracking furnace 90 thru line 91 where the hydrocarbon feed is subjected ice to cracking in tube coil 92. The partially cracked hot eluent is passed thru line 93 into feed injection tube 20 for injection axially thru combustion chamber 14 into reaction chamber 10.

In the event oxygen is injected with the axial feed, this gas may be introduced thru line 94 to preheater 95 and thence into line 96, or it may bypass heater 95 and pass thru line 97 into line 96.

Operation in accordance with the invention comprises injecting a mixture of natural gas (or other fuel gas) and air or oxygen wherein the amount of oxygen is in the range of 50 to 140 percent and, preferably, 90 to l20 percent of theoretical for complete combustion, is preferably preheated and charged to the tangential burners through burner tubes 32 to provide tunnel temperatures up to 3500' F. and sufficient to heat the axial feed to the desired temperature. It is preferred not to heat the air or oxygen in admixture with the fuel gas because of the explosion hazard. The oxygen supply may be heated in admixture with steam,`in the event steam is utilized in the tangential feed.

The axial feed comprising hydrocarbon and steam is preheated in heater or tube cracker 90 to convert paraflins to unsaturates before introducing the hot effluent from line 93 into injection tube 20. The steam admixed with the feed should be in the range of to 125 volume percent of the hydrocarbon. lt is preferred to maintain the steam in the axial feed in the range of 25 to 100 volume percent of the hydrocarbon. This feed is heated preferably to a temperature in the range of 800 to 1600 F. so as to crack and upgrade a substantial proportion of the hydrocarbon in the feed. While axial hydrocarbon feed may contain unsaturates, it is preferred to utilize aliphatic paratlins because of their relative cheapness. lt is recognized that unsaturates convert more readily to ethylene and acetylene, but the cost of these hydrocarbons is substantially greater than the cost of corresponding parains. Suitable parains include methane, ethane, propane, butane, pentane, hexane and other available hydrocarbon stocks containing substantial amounts of these parains such as naphtha, kerosene, and gas oils. The parafiins may be introduced singly in high concentration or in admixture with each other or with unsaturates.

The axial feed cracked by heating to a temperature in the range of 1000-1600" F., and preferably in the range of 1400 to 1600 F., containing a substantial proportion of unsaturates due to the precracking, enters combustion zone 14 surrounded by spiralling combustion gas therein and passes into reaction chamber 10 surrounded by a blanket of spiralling combustion gas adjacent the refractory wall 12. In passing through reaction zone l0, the axial feed is heated to the desired range to produce the desired acetylene and/or ethylene and the effluent is quenched in quenching means 56 by the water injected through spray and by water circulating through jacket 58. The effluent from chamber 10 is quenched to a temperature below reaction temperature which is generally below 800 F. The quenched effluent is then passed through line into conventional product separation means 72 from which the various constituents are separated in known manner and recovered as desired.

The quantities and rates of flow of the tangential and axial feeds are regulated to produce the optimum temperatures and reaction times for any particular feed to produce the optimum or maximum amounts of the desired products. Reaction time is very short in order to avoid overcracking and decomposition to carbon and hydrogen and is usually in the range of 0.5 to 0.001 second and even less. The reaction time depends upon the feed, the temperature in the reaction zone, and the product desired. Reaction time may be calculated in accordance with the equations set forth in my U.S. Patent 2,750,- 434, referred to supra.

When steam is included in the tangential feed, the volume ratio of steam to O2 is in the range of 1:1 to 8:1 and it is preferred to preheat the steam -03 mixture to the range of 800 to 1600 F.

The advantages of the invention are illustrated by the following examples which are to be considered illustrative and are not to be construed to unduly limit the invention.

EXAMPLE I Butane was pyrolytically converted to acetylene in substantial yield in a 3 inch tangential reactor at atmospheric pressure. The reactor was constructed in accordance with the drawing, precombustion chamber 14 being l1 inches in diameter and 4 inches long, while chamber 10 was 25 inches in length and 3 inches in diameter. Natural gas was used for the tangential fuel because of its availability and cheapness. A number of runs under different conditions were made and four of these runs which are typical are presented in Table I below.

The axial feed was preheated and cracked by being passed through a tube furnace prior to introduction to the reactor. In run l, no steam was included in the axial feed. In run 2 the effect of mixing 25 volume percent steam with the butane may be seen. There was an 4increased concentration of the acetylene in the effluent and a substantial reduction in coking in the quencher. The duration of the run at equilibrium conditions was about 8 hours in each instance. In run 3 the volume of steam was doubled but there was no significant improvement in results. However, this run was of only 8 hours duration and it is possible that over longer periods of operation, higher steam concentration may result in further reduction in coking in the quencher. In run 4 steam was included in the tangential feed and this feed was preheated to 1015 F. The acetylene concentration was slightly higher than without air preheat and the yield was slightly lower.

Table I Axial Taugentlal Oletn conc. Reactor preheat Butane Run No. Butane Steam, Feed pre- S'team and Tunnel pressure etlluent, destroyed rate, percent heat, F. Gas rate, Air rate, Steam rate, air preheat tempcrap.s.l.a. vol. percent ln preheater based on c.f.h c.f.h. c.!.h. F. ture, F.

butane 1 83. 2 1, 425 680 7, 470 4l. 8 2 83.0 25 1. 450 69D 7. 470 44. 4 3.--.---- 92.0 50 1, 455 680 7. 470 t 44. 1 63.0 8l. 3 25 1, 440 500 5, 900 l, 500 l, 025 2, 900 13. 2 43. 4 70. 3

Reactor etlluent composltlon-mol/peroent Acetylene ylel weight Run N0. percent,

0,13', CH4 CIH H; CO; CO N Argon CIH; CiHq Methyl Di-acet- Vinyl CH. based on acetylene ylene acetylene leed 5. 0 4. 7 2. 4 12. 2 6.0 6. 0 62.2 0. 8 0.1 0. l 0. 2 0. 3 0.? 0.1 39. 1 5. 3 4. l. 1. 7 11. 8 6. 7 5. 1 63. 5 0. 7 0. I 0.1 0.2 0.3 0.2 Tr. 40. 8 5. 3 4. 6 2. l l2. 1 6. 5 5. 5 62. l 0. 8 0. l 0. 1 0.2 0.3 0. 1 0. 2 37. 7 5. 5 4. 6 1. 3 17. 2 6. 5 4 68. 5 37* 5 EXAMPLE II Runs were made to convert propane to acetylene and ethylene in the reactor of Example I, again using natural gas and air as the tangential fuel. The data representing ing said feed; said feed is passed, initially surrounded by a helically moving annular blanket of said combustion gases, into said second reaction zone; said feed is heated by said combustion gases to a temperature in the range typical runs are set forth in Table Il as runs 5, 6 and 7. 5 of 1500. to 350cv F' to cause same to react and form The composition of the propane feed utilized in the runs predominantly unsatuated hyqmcarbons; .the emuem is as fouowsfrom said second reaction zone is quenched in a quench zone to a temperature below reaction temperature; and Run 5: Percent said unsaturated hydrocarbons are recovered; the im- CaHs 67-8 10 provement comprising including at least 50 volume per- CaHs 0-3 cent of aliphatic paran hydrocarbon in said feed; heatiCiHio 18-7 ing said feed in the preheating step toa temperature in nCiHio 13-2 tha rango of about 10oo to i600' F. in admixttna with Run 6: steam in the range of 10 to 125 volume percent of the CsHs 92-3 15 hydrocarbon feed so as to crack and convert a greater C2Hc 2-6 proportion of said paladin-hydrocarbon to olefin hydro- 1C4Hio 3-4 carbon than would occur without said steam before passnCHN 1'4 ing the preheated feed and steam to said irst reaction Run Z; 96 3 zone, whereby the amount of unsaturates in said efuent Il -II 3'4 20 is increased and carboif deposition in said tube cracker, gn 0 '2 in said second reaction zone and in said quench zone is, nCHu) 0 1 reduced.

2. The process of claim 1 wherein said feed comprises The runs show that results obtained from diierent conpredominantly C1 to C4 parans centran of Propane m the feed am not materially dif 3. The process of claim 1 wherein reaction conditions ferent. The propane feed rates were varied in the diermducing maximum yields of acetylene including a wm ent runs with higher rates showing higher ethylene yields. p tur i t1 st 1900. F ar maintained and met Iene The yield of acetylene plus ethylene was as high as about Pera e o a th e y 54 percent. In runs 5 and 6 there was no carbon deposis recovered from e uqsaturates tion in the reactor and greatly reduced carbon deposition 4' The Process of clam 3 wherem said feedfqns in the quencher compared with runs without steam in essemlally of C1 t0 C4 Pilratins and am steam 13 m the the axial feed. In run 7 there were a few small specks of range 0f 20 t0 100 Volume pement 0f the hydmcalbon carbon deposit in the reaction section 10. feed.

Table 1I A1131 Tongenuol m o enn Reactor etlluent composition-mol percent sA i e t a1t Egyl- Ru Pm a a aan siii. ...ist No' gila't ieri? gif, fiti, t'guuiiart'ip'iomuaat, ein. ont Cin. Ht co, co N. pratit, pgrtt,

agigc.f.h. c.f.h. surre, sulro, vol. onfd on eed pane s 86.0 25 1,520 oso 1,470 2,1m 2,360 37.5 5.1 4.3 1.o 13.3 se 5.3 64.4 31.9 ai in; ist a ist a itis in ias a: it it iii ii t: sa iii Variations and modicatom are possible within the 5. The pI'OCSS 0f Claim 4 wherein Said fed COmPI'SeS scope of the disclosure and claims to this invention, the principally buia-Ilo essence of which comprises precracking a hydrocarbon 6 Th PIOGGSS 0f Clalm 4 WhGNm wd fd 60111D1193 feed containing a substantial proportion of aliphatic parprincipally propane. ain, such as at least 50 volume percent, in admixture 7 Tho PfOSS 0f Cla lm 1 Whhmll jlltxftll' 0f Steam with at least 10 volume percent steam based upon the and air in a volume ratio of steam to air m the range of hydrocarbon food so as to convert pal-aging to olons 1:1 to 8:1 is preheated to an elevated temperature in the and, then, pyrolytieally converting the resulting feed to rangol of 800 to 1600 F. and mlotttfd Wlth Hamai SaS unsaturates comprising acetylene and ethylene in a tanaS Salti C0t nbl1 S1b1 mlxttlr, tho 0s 111 Said wmbllstble .gantialiy fired reactor, wherein the food is heated and mixture being 1n the ranse of IQ to 90% of the theoretical reacted within a helically moving annular blanket of oomamount for complete combustion of the f hel therein. bastion gases as it passes thru tha reaction zone. 'nie 8- The prooss of claim 7 wherein reaction conditions invention effects improved yields of ethylene and acetylene Pl'OdtlCmg mallmum Ylelds 0f acetylen, including a illfrom relatively cheap'parans and also decreases the 00 pramI0fat1a5t1900 F-,alemallllallled and afylelle carbon deposition in the reactor and in the quench cham- 1S ICCUVeId from the UIlSalll'ttS- ber at the gluem end of the Nador, 9. The process of claim 1 wherein reaction conditions 1 claim; producing maximum yields of ethylene, including a tem l. In a process wherein a hydrocarbon feed is pre- Penn-1 m the; fang" f 1500m 1900 F" an maintained heated in a tube cracker and passed in vapor form axially and cthylem s rovercd from the magnate" into a iirst cylindrical reaction zone of greater diameter than its length, contiguous to and coaxial with a second References Cited m the me of uns patent cylindrical reaction zone of lesser diameter and greater UNITED STATES PATENTS length; a combustible mixture of gaseous fuel and oxidant 2,750,420 Hepp June .12, 1956 are injected tangentially into said iirst reaction zone; said 2,750,434 Krejci lune l2, 1956 2,790,838 Schrader Apr. 30, 1957 mixture is burned to form hot combustion gases for heat- 

1. IN A PROCESS WHEREIN A HYDROGEN FEED IS PREHEATED IN A TUBE CRACKER AND PASSED IN VAPOR FORM AXIALLY INTO A FIRST CYLINDRICAL REACTION ZONE OF GREATER DIAMETER THAN ITS LENGTH, CONTIGUOUS TO AND COAXIAL WITH A SECOND CYLINDRICAL REACTIOIN ZONE OF LESSER DIAMETER AND GREATER LENGHT; A COMBUSTIBLE MIXTURE OF GASEOUS FUEL AND OXIDANT ARE INJECTED TANGENTIALLY INTO SAID FIRST REACTION ZONE; SAID MIXTURE IS BURNED TO FORM HOT COMBUSTION GASES FOR HEAT ING SAID FEED; SAID FEED IS PASSED INTIALLY SURROUNDED BY A HELICALLY MOVING ANNULAR BLANKET OF SAID COMBUSTION GASES INTO SAID SECOND REACTION ZONE; SAID FEED IS HEATED BY SAID COMBUSTION GASES TO A TEMPERATURE IN THE RANGE OF 1500 TO 3500*F. TO CAUSE SAME TO REACT AND FORM PREDOMINANTLY UNSATURATED HYDROCARBONS; THE EFFLUENT FROM SAID SECOND REACTION ZONE IS QUENCH IN A QUENCH ZONE TO A TEMPERATURE BELOW REACTION TEMPERATURE; AND SAID UNSATURATED HYDROCARBONS ARE RECOVERED; THE IMPROVEMENT COMPRISING INCLUDING AT LEAST 50 VOLUME PERCENT OF ALIPHATIC PARAFFIN HYDROCARBON IN SAID FEET; HEATING SAID FEED IN THE PREHEATING STEP TO A TEMPERATURE IN THE RANGE OF ABOUT 1000* TO1600*F. IN ADMIXTURE WITH STEAM IN THE RANGE OF 10 TO 125 VOLUME PERCENT OF THE HYDROCARBON FEED SO AS TO CRACK AND CONVERT A GREATER PROPORTION OF SAID PARAFFIN-HYDROCARBON TO OLEFIN HYDROCARBON THAN WOULD OCCUR WITHOUT SAID STEAM BEFORE PASSING THE PREHEATED FEED AND STEAM BEFORE PASSZONE, WHEREBY THE AMOUNT OF UNSATURATES IN SAID EFFLUENT IS INCREASED AND CARBON DEPOSITION IN SAID TUBE CRACKER, IN SAID SECOND REACTION ZONE AND IN SAID QUENCH ZONE IS REDUCED. 